1. Field of the Invention
The present disclosure generally relates to a protective layer setting unit for applying a protective agent to an image carrying member used in an image forming apparatus employing electrophotography and a process cartridge having the protective layer setting unit, and more particularly, to a method of evaluating a surface condition of a image carrying member coated with a protective agent not including a metal component.
2. Description of the Background Art
Typically, an image forming apparatus using electrophotography produces an image by sequentially conducting a series of processes, such as a charging process, an exposure process, a developing process, and a transfer process to a photoconductor such as an OPC (organic photoconductor). After conducting the transfer process, by-products generated by discharging during the charging process or toner particles remaining on the photoconductor are removed by a cleaning process. Such cleaning process can be conducted by using a cleaning blade, such as a rubber blade, which has a relatively simple and inexpensive structure but which cleans well.
However, such cleaning blade has a short lifetime and itself reduces the useful life of the photoconductor because the cleaning blade is pressed against the photoconductor to remove residual materials remaining on the photoconductor. More specifically, frictional pressure between the cleaning blade and the photoconductor abrades the rubber blade and a surface layer of a photoconductor.
Further, small-sized toner particles, used for coping with demand for higher quality images, may not be effectively trapped by such a cleaning blade, referred to as “passing of toner” or “toner passing.” Such toner passing is more likely to occur by insufficient dimensional or assembly precision of the cleaning blade or when the cleaning blade vibrates unfavorably due to an external shock or the like. If such toner passing occurs, desired higher quality images may not be produced.
Accordingly, to extend the lifetime of the photoconductor and to produce higher quality images over time, frictional pressure on the photoconductor or cleaning blade needs to be reduced and cleaning performance of the photoconductor needs to be enhanced, by which degradation of the photoconductor or cleaning blade can be reduced and the aforementioned “toner passing” can be reduced.
Given the need for such frictional pressure reduction and cleaning performance enhancement, in general, a lubricant is applied to the photoconductor to form a lubricant layer on the photoconductor using the cleaning blade. Such lubricant layer can protect the surface of the photoconductor from an effect of frictional pressure caused by the cleaning blade pressing against the photoconductor, which abrades the photoconductor, or from a discharge energy effect during a charging process, which degrades the photoconductor. Further, the photoconductor having such lubricant layer can enhance lubricating performance of the photoconductor surface, by which an unfavorable vibration of cleaning blade can be reduced, and thereby toner passing amount can be reduced.
Such lubricating and protection performance of the lubricant is affected by an amount of lubricant applied on the photoconductor, requiring that an application amount of lubricant be carefully controlled. If the application amount of lubricant is too small, the aforementioned photoconductor abrasion by frictional pressure, photoconductor degradation by charging process, and toner passing may not be effectively reduced. Accordingly, the state of the lubricant application on the photoconductor, such as application amount, needs to be measured.
In general, a metallic soap such as zinc stearate is used as the lubricant. However, zinc stearate may adhere to a charge roller of an image forming apparatus and cause unfavorable charging, which may result in a lower quality image, for example an image containing black streaks. When zinc stearate is used as the lubricant, a lubricant amount of zinc stearate applied to a photoconductor is analyzed using XPS (X-ray photoelectron spectroscopy), in which the amount of zinc element as a percentage of all elements on the surface of the photoconductor is measured.
In XPS analysis, elements other than hydrogen existing in a top and a sub-surface of a sample can be detected. When an OPC (organic photoconductor) coated with zinc stearate is analyzed using XPS, an element amount profile detected by XPS varies depending on a coating amount or coating ratio of zinc stearate. For example, when no zinc stearate is applied to the OPC, the element amount profile shows an element distribution of the OPC itself, whereas when zinc stearate is applied to the OPC, the element amount profile shows a mixture of the element distribution of the OPC and the element distribution of the zinc stearate. If the zinc stearate is applied to the entire surface of the OPC (i.e., OPC is 100% coated with zinc stearate), the element amount profile only shows the element distribution of the zinc stearate, and therefore an upper limit of zinc amount or ratio on the OPC becomes a zinc amount or ratio of the zinc stearate itself. Accordingly, when zinc stearate, which has a chemical composition of C36H70O4Zn, coats the entire surface of the photoconductor, theoretically the ratio of zinc to all elements should be 2.44%, which is the ratio of zinc to all the elements in zinc stearate (C36H70O4Zn) excluding hydrogen.
However, XPS or X-ray fluorescence (XRF) analysis is preferably used for detecting metal components. Therefore, when a protective agent such as paraffin, which does not contain metal, is applied to the OPC, XPS analysis shows only peak values for carbon (C) and oxygen (O), meaning that the amount of protective agent applied to the photoconductor may not be effectively measured. Inductively coupled plasma (ICP) spectroscopic analysis, which can be similarly used to evaluate the amount of protective agent applied to the photoconductor by detecting the metal component in the protective agent, also suffers from the same drawback and cannot be used to effectively measure the amount of a protective agent such as paraffin that does not contain metal.
Further, an attenuated total reflection (ATR) method is known for analyzing organic materials. In the ATR method, infrared absorption spectrum is measured using total reflection. Specifically, an ATR prism having a higher refractive index is closely contacted against a sample, an infrared (IR) light is irradiated to the sample via the ATR prism, and then an outgoing light from the ATR prism is analyzed spectrometrically. The infrared light can be totally reflected at a contact face of the ATR prism and the sample (i.e., total reflection) when the infrared light is irradiated to the ATR prism with a given angle or more, wherein such given angle is determined based on a relationship of the refractive index of the ATR prism and the sample. During such IR light irradiation, the IR light reflects from an internal surface of the ATR prism and generates an evanescent wave which projects orthogonally into the sample. Some of the energy of the evanescent wave is absorbed by the sample and the reflected IR light is attenuated and received by a detector, by which absorption spectrum of the sample can be obtained.
The ATR method is useful because it can accommodate various samples because an absorption spectrum of the sample can be measured by contacting a portion of the sample against the ATR prism. For example, absorption spectrum of a thick sample or low-transmittance sample can be measured if such sample can be closely contacted to the ATR prism. Moreover, in the ATR method, a functional group in the sample can be determined based on wavenumber corresponding to absorbed infrared light, and therefore the ATR method is widely used for qualitative analysis. However, because a peak intensity of absorption spectrum varies due to the pressure with which the sample is pressed against the ATR prism, and therefore the ATR method may not be used so often for quantitative analysis.
Recently, a charging process for electrophotography has been employing AC charging using a charge roller, in which an alternating current voltage is superimposed on the direct current voltage. Such AC charging has many advantages, in that it can charge a photoconductor more uniformly, can reduce generation of oxidizing gas, such as ozone and nitrogen oxide (NOx), and can contribute a size reduction of an image forming apparatus, for example.
However, a photoconductor may be acceleratingly degraded because a discharge of positive and negative voltages repeatedly occurs with a frequency of the applied alternating current voltage, such as several hundred to several thousand times per second between a charging device and the photoconductor. Such degradation of the photoconductor can be reduced by applying a lubricant, such as metallic soap, on the photoconductor because such lubricant can absorb discharge energy of the AC charging so as to prevent the discharge energy effect to the photoconductor.
Such lubricant (e.g., metallic soap) itself also may be decomposed by the AC charging. More precisely, the metallic soap is not decomposed completely but to a lower molecular weight fatty acid, and a friction pressure between the photoconductor and a cleaning blade increase as the lubricant is decomposed. Such fatty acid and toner may adhere to the photoconductor as a film which degrades image resolution, abrades the photoconductor, and causes uneven image concentration.
In light of such phenomenon, a greater amount of metallic soap may be applied on the photoconductor so as to effectively coat a surface of the photoconductor with metallic soap even if some fatty acid may be generated. However, in actuality only some of the metallic soap may actually adhere to the photoconductor even if the photoconductor is supplied with a greater amount of metallic soap, and most of the metallic soap applied on the photoconductor may be transferred with toner, or removed with waste toner, for example. Accordingly, the metallic soap may be consumed rapidly, and the metallic soap may need to be replaced with new metallic soap in a time period, which may be shorter than a lifetime of the photoconductor.
In view of such drawback, instead of using metallic soap, higher alcohol having a greater carbon number, such as from 20 to 70, is used as a main component of a lubricant (or protective agent) in one related art. When such lubricant is applied to a photoconductor, higher alcohol accumulates on a leading edge of a cleaning blade as indefinite-shaped particles, and such lubricant has surface wet-ability with the surface of photoconductor, by which such lubricant can be used for a long period of time.
However, if higher alcohol is used as lubricant, one molecule of higher alcohol may coat a relatively larger area on the photoconductor, and thereby density of higher alcohol molecules absorbed on the photoconductor per unit area may become smaller (i.e., smaller molecular weight per unit area), which is not preferable from a viewpoint of reducing the electrical stress of the AC charging to the photoconductor.
Another related art proposes using powder of an alkylene bis-alkyl acid amide compound as a lubrication component to supply powder to a surface boundary between a photoconductor (or image carrying member) and a cleaning blade, contacting the photoconductor, so as to provide smooth lubrication effect on the surface of the photoconductor for a long period. However, if the lubricant having nitrogen atom is used, the lubricant itself may generate decomposition products having ion-dissociative property, such as nitrogen oxide and a compound having ammonium when the lubricant is subjected to the electrical stress of AC charging. Such products then intrude into a lubrication layer, reducing resistance of the lubrication layer under a high-humidity condition and possibly causing grainy images as a result.
It is known that a protective agent having paraffin as a main component can protect a photoconductor from the electrical stress of AC charging, can reduce a frictional pressure between the photoconductor and a cleaning blade, and can remove toner remaining on the photoconductor well, for example. Further, the protective agent having paraffin may not generate so much fatty acid even if the protective agent is oxidized by the electrical stress of AC charging, which is preferable for reducing a variation of the frictional pressure between the photoconductor and the cleaning blade.
However, when image forming operations are repeated by using the protective agent having paraffin, abnormal images, such as streak image, are produced in some cases, wherein such abnormal images may be caused by abrasion of the photoconductor and the cleaning blade. Based on research, probability of such abnormal images varies among product lots of protective layer setting units. Research was further conducted for photoconductors, which produced and did not produce abnormal images, to find that the abnormal images occurred on an area where a layer thickness of the photoconductor was relatively thinner or an area where toner was attracted with a greater amount on the photoconductor. However, root causes of such abnormal images are known yet.
As mentioned, paraffin can be effectively used as a protective agent instead of metallic soap. However, when a protective agent, such as paraffin, not containing metal component is applied to the OPC, XPS or XRF analysis show only peak values for carbon (C) and oxygen (O), and therefore the amount of protective agent applied to the photoconductor may not be effectively evaluated. Further, ICP spectroscopic analysis may not be suitable for effectively evaluating the amount of protective agent, not containing metal component, applied to the photoconductor because the ICP spectroscopic analysis is also used for detecting a protective agent (e.g., metallic soap) having metal component. If the amount of protective agent on a photoconductor cannot be effectively evaluated, a photoconductor having an insufficient amount of protective agent may be assembled in a process cartridge or an image forming apparatus, and such photoconductor can cause image quality degradation.
As such, a conventional analysis method may not be suitable for detecting an amount of a protective agent, such as paraffin, not including a metal component, and therefore a method of effectively evaluating a surface condition of a photoconductor coated with a protective agent not including a metal component is desired.